Is this still up-to-date with the way GHC/GHCi work internally? Then I'll certainly check it out.

I think it isn't since STG is pretty much different with the G-machine describes in the book. The original paper about Spineless Tagless G-machine is here [1]. It is quite verbose. Recent paper "How to make a fast curry: push/enter vs eval/apply" [2] is much smaller, but it represents more recent state of GHC and can be read independently with the first paper. The book from 1987 [3] is a very good and detailed overview of the subject and it is valuable as itself, no matter how it actually implemented now. -- 1. https://research.microsoft.com/users/simonpj/papers/spineless-tagless-gmachi... 2. https://research.microsoft.com/users/simonpj/Papers/eval-apply/index.htm 3. https://research.microsoft.com/users/simonpj/Papers/slpj-book-1987/index.htm